Here's the AMA Class/engine displacement chart.
Chapter 1, Section 1.3, Subsection J - 2
View attachment 1430
Get the 125 and if you're body is up for you can run 3-4 classes.
Damn that would be brutal, you'd finish one moto and then have to go line up for the next one right away.
on pyramid valleys 2010 season points page there is a kid who raced 4 classes yes all in one day and only missed 1 day the whole season + he got 1st place accept one 125 race he got like 4th or 5th